An automatic drain for draining a liquid component, such as water and oil, contained in the compressed air is provided to an air pressure line through which compressed air is supplied from an air pressure source to air-supplied components such as pneumatic equipment.
A float-type automatic drain, as described in Japanese Patent Application Laid-Open Publication No. 2005-155727, includes a collection container in which liquid is collected, together with a tiny solid material contained in compressed air. A valve seat having a discharge hole and a drain valve that opens and closes the discharge hole are attached to a bottom of the collection container. When the amount of liquid collected in the collection container reaches a predetermined amount, the discharge hole is automatically opened by the drain valve.
The drain valve is provided to a piston which is attached in a cylinder and movable in an axial direction. A float is disposed on the outside of the cylinder. When the amount of accumulation of the collected liquid reaches the predetermined amount, a vent valve is opened by the float, which causes air to be supplied into a piston chamber in the cylinder. Being subjected to the force of this incoming air, the piston in the piston chamber drives the drain valve. As a result, the discharge hole is opened, which causes the liquid collected in the collection container to drain out of the discharge hole.
To discharge air in the piston chamber to the outside, an orifice, i.e., bleed hole is provided to the drain valve. A length of time required for discharging the liquid to the outside corresponds to the length of time required for discharging air in the piston chamber to the outside via the orifice. An increase in inner diameter of the orifice reduces the length of time required for discharging air in the piston chamber to the outside. In such a case, therefore, the drain valve is closed before the entire liquid collected in the collection container is discharged to the outside.
Japanese Utility Model Application Laid-Open Publication No. 51-43935, microfilms discloses a drain ejector including a valve stem having a valve attached to a lower end of the valve stem, the valve working as a drain valve. A fixed orifice communicating with a back pressure chamber is disposed on an upper end of the valve stem, and the valve's open interval of time is extended by a spring link.
Japanese Examined Patent Application Publication No. 45-36182 discloses a servo and an automatic liquid discharge mechanism. A piston serving as a partition member and a coil spring for applying a spring force to the piston are incorporated in the servo. The servo and a float disposed on top of the servo are housed in the container of the automatic liquid discharge mechanism. The partition member is provided with an arbor serving as a drain valve, and the arbor has a bleeding hole in which a starting bar is placed to be axially movable. An upper end of the starting bar extends to the inside of the float. The starting bar thus moves up and down depending on the upward and downward movement of the float. The upward and downward movement of the starting bar prevents entry of foreign matters into the bleeding hole.